The following references are believed to represent the state of the art:
US Published Patent Application 2011/0230209 of Kilian;
US Published Patent Application 2012/0066035 of Stranger, et al.;
US Published Patent Application 2012/0131094 of Lyons, et al.;
US Published Patent Application 2012/0190386 of Anderson;
US Published Patent Application 2012/0215640 of Ramer, et al.;
U.S. Pat. No. 6,269,246 to Rao, et al.;
U.S. Pat. No. 7,042,391 to Meunier, et al.;
U.S. Pat. No. 7,194,278 to Cook; and
U.S. Pat. No. 8,140,094 to Morgan, et al.